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Fishery Bulletin 95(2), 1997 
tically all year. The main spawning periods, however, 
are in the spring (April-May) along the northern 
coast of Spain (Cantabrian Sea) (Sola et al. 4 ) and in 
winter (December^January) off the northern Portu- 
guese coast (Re et al., 1990). Thus, in a given year, a 
wide range of likely birthdates exist. Depending on 
the particular biotic and abiotic conditions that af- 
fect survival during the prerecruitment period, the 
abundance and the age composition (birthdate dis- 
tribution) of recruits will be restricted, however, to a 
relatively short period. 
An important part of the present study was initi- 
ated through Spanish-USA collaboration (Anony- 
mous, 1990) within the framework of the Sardine 
Anchovy Recruitment Project (SARP). The work car- 
ried out in this program continued for the next 3 years 
under the auspices of a European program that also 
sponsored research on the sprat Sprattus sprattus 
in the German Bight and the anchovy Engraulis 
encrasicolus within Portuguese estuaries. The origi- 
nal aim of this project was to identify the biological 
and environmental factors affecting interseasonal 
larval mortality of short-lived coastal pelagic fish. 
Birthdate analysis is one of the more relevant tools 
for the study of recruitment processes (Campana and 
Jones, 1992). Birthdates of juvenile fishes were first 
calculated by Methot (1983) who showed that the 
data can be used to determine periods of high sur- 
vival. This technique is a key element in the work of 
SARP, i.e. to test the critical survival-period hypoth- 
esis (Hjort, 1914 and 1926) and its later variants 
(Cushing, 1975; Lasker, 1981; Parrish et al., 1981). 
Only one paper, in which this technique was applied, 
is available for the area studied (Alvarez and Butler, 
1992). It shows that birthdates of surviving fish oc- 
curred at the beginning of a period of calm weather 
in May and is consistent with Lasker’s (1981) stable- 
ocean hypothesis. 
The aims of the present work were 1) to calculate 
the birthdate distribution of recruits in the stock of 
the Atlanto-Iberian sardine in 1992, as inferred from 
daily otolith growth increment analysis; 2) to relate 
the birthdate distribution of recruits to environmen- 
tal conditions during earlier development stages; and 
3) to verify the previous hypothesis that sardine re- 
cruits in the Galician area originate in the Canta- 
brian Sea. 
Material and methods 
Age determination 
Juvenile sardines were sampled fortnightly, 30 June- 
19 November 1992, from landings of the commercial 
purse-seine fleet at the ports of Vigo and La Coruna 
(Fig. 1), providing a total of 22 samples, each of 50 
specimens. These ports are located in the area of re- 
cruitment of the Atlanto-Iberian sardine (age-0 fish) 
(Anonymous 1 ). A subsample of ten individuals was 
taken at random from each sample for birthdate 
analysis from counts of the daily growth-ring incre- 
8°W 7° 6° 
Figure 1 
Map of the northwestern Iberian peninsula showing sampling ports (dots) 
and area of distribution of age-0 sardines, Sardina pilchardus (shadowed), 
during the 3rd and 4th quarters in 1992 (redrawn from Anonymous, 1993). 
